The main issue with WebM is that the player doesn't support all the features that their Flash player does (e.g. advertising and annotations). And this will not

The main issue with WebM is that the player doesn't support all the features that their Flash player does (e.g. advertising and annotations). And this will not necessarily make the web less patent encumbered. Just like companies extract patent licensing fees from companies making use of Android, companies will probably try to extract licensing fees from companies using WebM. The problem isn't the formats so much as the patent system.